Boundary Layer Aerosol Sources and Cloud Interactions in the Summertime Remote Arctic

Aerosol concentrations at the surface in the remote Arctic are at a minimum in the summer and, in extreme cases, sometimes reach numbers so low that clouds are unable to form. The presence, or lack thereof, of clouds has major impacts on the radiation budget, and so understanding the aerosol sources is critical to forecasting the weather and climate of the region. In this study, we use a combination of observations and modeling to investigate the potential importance of free tropospheric aerosols to the boundary layer aerosol budget and the role of clouds in modulating this importance. Previous studies have suggested that the importance is low. However, observations from the Arctic Summer Cloud Ocean Study (ASCOS) reveal that much higher aerosol concentrations can sometimes be found just above the boundary layer top. LES simulations suggest that when these enhanced aerosol concentrations are present, they can easily be entrained into the boundary layer. The net flux of aerosol particles is also modulated by the clouds themselves through activation of particles above the boundary layer top and regeneration below cloud base. When enhanced aerosol concentrations above the boundary layer top are present, the surface aerosol properties may not be a good indicator of aerosol properties that impact the cloud layer.